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The derivative of cos–1(2x2 – 1) w.r.t. cos–1x is ______.

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Question

The derivative of cos–1(2x2 – 1) w.r.t. cos–1x is ______.

Options

  • 2

  • `(-1)/(2sqrt(1 - x^2)`

  • `2/x`

  • 1 – x2 

MCQ
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Solution

The derivative of cos–1(2x2 – 1) w.r.t. cos–1x is 2.

Explanation:

Let y = cos–1(2x2 – 1) and t = cos–1x

Differentiating both the functions w.r.t. x

`"dy"/"dx" = "d"/"dx" cos^-1 (2x^2 - 1)` and `"dt"/"dx" = "d"/"dx" cos^-1x`

⇒ `"dy"/"dx" = (-1)/sqrt(1 - (2x^2 - 1)^2) * "d"/"dx" (2x^2 - 1)` and `"dt"/"dx" = (-1)/sqrt(1 - x^2)`

= `(-1.4x)/sqrt(1 - (4x^4 + 1 - 4x^2)` and `"dt"/"dx" = (-1)/sqrt(1 - x^2)`

= `(-4x)/sqrt(1 - 4x^4 - 1 + 4x^2)`

= `(-4x)/sqrt(4x^2 - 4x^4)`

= `(-4x)/(2xsqrt(1 - x^2)`

⇒ `"dy"/"dx" = (-2)/sqrt(1 - x^2)`

Now `"dy"/"dx" = ("dy"/"dx")/("dt"/"dx")`

= `((-2)/sqrt(1 - x^2))/((-1)/sqrt(1 - x^2))`

= 2.

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Chapter 5: Continuity And Differentiability - Exercise [Page 115]

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NCERT Exemplar Mathematics Exemplar [English] Class 12
Chapter 5 Continuity And Differentiability
Exercise | Q 93 | Page 115

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